Submarine craft

ABSTRACT

A submarine craft with hydraulic energy transmission system which receives its energy from a converter which converts electrical energy to hydraulic energy. The hydraulic energy is subsequently employed for driving at least one propeller by an axial piston engine; for fine adjustment of a buoyancy system of the craft; and for operating trim devices to alter the center of gravity of the craft. A sliding ring seal is employed to seal the shaft driving the propeller towards the interior of the hydraulic motor. A leak water collecting chamber sealed against the outboard water is provided on that side of the sealing ring which faces the water and is connected to a leak-water tank whose internal pressure is maintained at a predetermined value.

United States Patent 1 1 Haas 1451 Oct. 1, 1974 SUBMARINE CRAFT [75]Inventor:

[73] Assignee: Bruker-Physik AG, Karlsruhe,

Germany 22 Filed: Dec. 30, 1971 21 Appl. No.: 213,882

Jorg Haas, Neureut, Germany 115/34 R, 34 A, 18 E; 308/363 3,665,8845/1972 Gustafson 114/16 E Primary ExaminerTrygve M. Blix AssistantExaminerGalen L. Barefoot Attorney, Agent, or FirmCraig & Antonelli [57] ABSTRACT A submarine craft with hydraulic energy transmission systemwhich receives its energy from a converter which converts electricalenergy to hydraulic energy. The hydraulic energy is subsequentlyemployed for driving at least one propeller by an axial piston engine;for fine adjustment of a buoyancy system of the craft;

5 References Cited and for operating trim devices to alter the center ofUNITED STATES PATENTS gravity of the craft. A sliding ring seal isemployed to seal the shaft driving the propeller towards the interior ai of the hydraulic motor. A leak water collecting cham- 10/1942 gg gg308/36'3 ber sealed against the outboard water is provided on 32023888/1965 115/34 that side of the sealing ring which faces the water and3:301:209 1/1967 Caldwell 114/16 E is connected 3 leak-Water tank Whoseinternal P 3,467,050 9/1969 Herbert 308/363 sure is maintained at a p ermined value. 3,587,511 6/1971 Buddrus 115/34 A 3,635,183 1 1972Keatings 114/16 R 7 Clams, 3 Drawmg 27 --L Q r II II I? It? PAYENIEBUBTH914 3838.654 I mm 30v 5 INVENTOR 35R 6 HAA 5 BY Gala, MtowzQQc QH-LQQATTORNEYS SUBMARINE CRAFT The present invention relates to a submarinecraft having a tight pressure hull and at least one propeller which isdriven by a motor supplied with energy from an energy source providedfor that purpose.

In conventional submarine craft, the various consumers are generallysupplied with energy in the form of electric power. The propellers bywhich the craft is propelled and/or manoeuvered are, for instance,driven by electric motors. These electric motors are usually locatedinside the pressure hull and the drive shafts are passed through thepressure hull in a sealed arrangement. This has the drawback that sealsfor rotating shafts must be provided with are subject to the outboardpressure which may be very high in some cases. Another drawback consistsin that the shafts and seals transmit the structure-borne noise of themotors to the pressure hull which acts like a resonant cavity radiatingthe noise toward the inside and outside. This noise radiation is ageneral nuisance and, in particular, a considerable stress and burdenfor the crew of the submarine craft. Prior art systems also includeoutboard electric motors whereby the drawbacks of passing the shaftsthrough the pressure hull are avoided. However, a drawback which allelectric motor drives have in common consists in that these have a veryhigh flywheel effect, which means that manoeuvring is difficult withelectric motors, because owing to their moment of inertia electricmotors will not stop instantly when they are switched off or will notattain their new speed or sense of rotation very quickly when they arereversed, thus impairing the manoeuvrability of the submarine craft.

I The outboard electric motors of the prior art are threephase a.c.motors which cannot be supplied directly from the battery aboard thecraft, but require either rotary converters or thyristor converterswhich latter tend to generate awkward voltage peaks in the supply systemof the craft.

It is the object of the present invention to provide an improved energysystem for submarine craft.

In accordance with the present invention, this object is accomplished byproviding the submarine craft with a hydraulic energy transmissionsystem which receives its energy from a converter fed by the energysource and supplies it to consumers and to which are connected hydraulicmotors which drive the propellers. A special advantage of the submarinecraft in accordance with the present invention consists in that it ishighly manoeuvrable because owing to their very low moment of inertia,which is only about one tenth of that of electric motors, the hydraulicpropulsion units respond.

very quickly to a reversal of the sense of rotation and a change inspeed. Speed and sense of rotation of a plurality of propulsion unitsmay be changed independently by means of spacesaving, uncomplicatedcommercially available hydraulic control components. An added advantageconsists in that the motor may be located outside the pressure hull,thus obviating the need of using seals for rotating shafts. Hydraulicmotors are insensible to moisture and energy may be supplied throughpipes and hoses. This affords the further advantage of precluding anytransmission of structureborne noise from the drive motor through theenergy supply line. If, in addition, the motor is connected to thesubmarine craft by an arrangement including flexible sound-deadeningelements, the transmission of structure-borne noise to the pressure hullcan be largely eliminated, which has the advantage that propeller,bearing and motor noise is kept away from the pressure hull so that thepressure hull no longer acts like a resonant cavity which radiates noisetoward the inside and the outside.

According to a preferred embodiment of this invention, electric storagebatteries are used as energy sources in a manner known per se and theconverter comprises an electric motor and a hydraulic pump. Theconverter may be designed as a totally enclosed unit housing the motorand the pump in its interior, in which case only the two electricfeeders for the motor and the two hydraulic lines leading to the pumpconnectionsare passed through the enclosure. Alternatively, the electricmotor driving the hydraulic pump may be replaced by a steam turbinewhich receives its energy from a nuclear reactor installed in the craft,for example.

However, the hydraulic energy transmission system not only serves todrive the propellers for propulsion and steering of the submarine craft,but, according to a preferred embodiment of this invention, enables asystem for fine adjustment of the buoyancy to be connected to it whichcomprises a tank into which water is admitted orfrom which water isexpelled by means of a hydraulic fluid to produce a corresponding changein buoyancy. Such a system is described in the copending applicationSer. No. 203,644 now abandoned. lt enables the effective weight of thecraft and, thus, its positive or negative buoyancy to be changed.According to a further embodiment of the invention, submarine tools andmanipulators located outside the pressure hull may be connected to, andoperated by, the hydraulic energy transmission systemfSuch tools may,for instance, include grapplers, scrapers, soil sampling devices and thelike with which a submarine craft employed for underwater work andresearch may be equipped. Preferably, the hydraulic energy transmissionsystem of this invention is adapted for connection of a trim device bymeans of which heavy masses may be shifted to alter the position of thecenter of gravity of the craft. Such a trim device is described in thecopending application Ser. No. 203,643 now abandoned.

Each propeller and its drive motor may be disposed with spaced relationto each other, connected only by a shaft. According to a preferredembodiment of the invention, each propeller is combined with theassociated drive motor into a single structural unit located outside thepressure hull, said structural units being connected to the pressurehull only by means of flexible rubber elements, such as rubber-bondedmetal bearings, and through hydraulic hoses. This embodiment affords theadvantages of greatly reduced noise and a very compact construction,because even a low-volume hydraulic motor will produce a very hightorque owing to the high pressures which it permits.

The invention permits the use of different types of hydraulic motorssuch as gear motors or vane-type motors. Preferably, however, the motorsdriving the propellers are of the axial piston type with the housingdirectly exposed to the water.

The shaft driving the propeller is preferably sealed towards theinterior of the motor by means of a sliding ring seal. A leak-watercollecting chamber sealed against the outboard water by means of afurther sealing arrangement is provided on that side of said slidingring seal which faces the water. This chamber is connected to aleak-water tank whose internal pressure is maintained at a predeterminedvalue. The internal pressure in this chamber may, for example, equal theatmospheric pressure existing at the water surface and inside thepressure hull. This ensures that on the one hand water leaking past theouter sliding ring seal will be drained without causing damage and thaton the other hand the lip seal sealing the interior of the motor willonly be subjected to the permissible pressure, since a predeterminedpressure is being maintained in the leak-water collecting chamber, sothat the said seal may attain the desired useful life.

In preferred embodiments of this invention, a propeller shaft bearing isprovided adjacent to the sliding ring seal and accommodated within thesame housing as said seal. The advantage consists in that thisarrangement results in a very compact construction. Although an overhungmounting of the propeller is possible, a preferred arrangement is one inwhich that part of the housing which encloses the leak-water collectingchamber is provided with a cylindrical extension carrying awater-lubricated bearing at its end. The propeller inclusive of themotor, if desirable is surrounded by a ring-shaped jacket which orientsthe stream of water displaced by the propeller and also protects thepropeller from damage by foreign matter.

According to preferred embodiments of this invention, flow controlvalves are provided in the hydraulic supply line of each drive motor tocontrol its speed and- /or sense of rotation. These flow control valvespermit a very accurate metering of the flow of hydraulic fluid and,thus, a very sensitive adjustment of the desired speed. Change-overvalves which are operated to reverse the sense of rotation are providedupstream or downstream of the flow control valves. The various valvesare preferably grouped together in a common housing block.

Further details and developments of the present invention will becomeapparent from the following description in which one embodiment of thisinvention will be explained by way of example with reference to theaccompanying drawing which shows this embodiment in a highly schematizedand simplified representation and in which FIG. 1 is a diagrammaticrepresentation of a submarine craft with a hydraulic energy transmissionsystem in accordance with the invention,

FIG. 2 shows a longitudinal section through a propulsion unit, and

FIG. 3 is a basic circuit diagram of a system in accordance with theinvention in which the control valves are represented by symbols.

The submarine craft has a pressure hull 1 shaped like a cylinder withhemispherical end sections. Inside the pressure hull there is providedan energy converter comprising a motor 2 and a pump 3 driven by saidmotor. The motor 2 is fed by an'energy source 4 which may be locatedinside or outside the pressure hull 1.

vThe suction end of the pump 3 is connected to a hydraulic fluid tank 5.Through a supply line 6, it delivers hydraulic fluid under high pressureto a control device 7 represented as a block. The control device 7accommodates a plurality of throttle valves and reversing valves whichsupply the fluid flow delivered through the supply line 6 to variousconsumers in accordance with a pattern which may be selected and changedas desired. A return line 8 returns any excess of hydraulic fluid fromthe control device 7 to the hydraulic fluid tank 5. In the embodimentshown by way of example, the control device 7 distributes hydraulicfluid to three hydraulic motors. One of these motors is part of apropulsion unit producing a thrust acting approximately along thelongitudinal axis of the pressure hull 1 while the two other motorsproduce a horizontal thrust.

Each motor is connected by two lines, one supply line and one returnline. The functions of the two lines may be reversed, thereby reversingthe sense of rotation of themotor. A flow control or metering valve isprovided in one of the two lines or, alternatively, upstream of thepoint at which the hydraulic fluid stream enters one of the two lines.The flow control or metering valve may also be combined with the controlvalve by means of which the functions of the two lines may be reversed.All these valves are accommodated in the control device 7. They may bemanually controlled or remotecontrolled, e.g. by electric power.

From the control device 7, two lines 9 lead to a hydraulic motor 10which is disposed outside the pressure hull 1 with a verticallyextending shaft. At the end of this shaft there is provided a steeringpropeller 11. The hydraulic motor 10 is located at the stern of thesubmarine craft. Similarly, a hydraulic motor 12 is provided outside thepressure hull l in the vicinity of the bow of the craft. This hydraulicmotor is connected to the control device 7 by means of two lines 13through which hydraulic fluid may be supplied and returned. At its freeend, the horizontally extending shaft of the hydraulic motor 12 carriesa steering propeller 14.

At the stern of the craft, there is provided a hydraulic motor 15 whoseoutput shaft 16 extends parallel to the longitudinal axis of thepressure hull 1 and, at its free end, carries a propeller 17 whichpropels the craft ahead and astern. The hydraulic motor 15 is connectedto the control device 7 by means of two lines 18 through which hydraulicfluid may be supplied and returned. From each of the motors 10, 12 and15 a leakwater line 19, 20 and 21 respectively leads to a leakwatercollecting tank 22 whose internal pressure equals the internal pressureof the pressure hull l which is always below atmospheric pressure,equalling atmospheric pressure only in the surfaced condition of thecraft.

All lines are passed through the pressure hull l in a pressure-tightarrangement. Inside the pressure hull, each line incorporates a shut-offvalve 23. Finally, each hydraulic motor 10, 12, 15 is connected to thehydraulic fluid tank 5 by means of a leakage line 24, 25 or 26respectively. These lines return any leakage of hydraulic fluid to thehydraulic fluid tank. Inside the pressure hull, these leakage lines arealso provided with shut-off valves 23.

The pressure which the pump 3 generates in the hydraulic system may beadjusted to a desired value by varying the amount of fluid delivered bythe pump. If the pump is an axial piston pump oran axial cylinderswashplate pump, its delivery may be varied by adjusting the stroke, orelse delivery may be varied by changing the speed at which the pump isdriven. However, a preferred arrangement is one in which the pressuregenerated in the system may be adjusted by means of an overflow valve 27which opens at a predetermined pressure and allows hydraulic fluid fromthe supply line 31 to flow into a leakage line 28 which leads to thehydraulic fluid tank, 5, the discharge section to which the overflowvalve is opened being such that the desired pressure is maintained inthe hydraulic system. When the pressure rises, the discharge section ofthe valve is increased, when the pressure drops, the discharge sectionis reduced. Such valves are well known in the art. In their simplestform they feature a piston which is exposed to the fluid pressure andbacked by a spring. When the pressure rises, the piston is displaced andthe spring compressed. Simultaneously, the piston opens a drain openingthrough which fluid may flow off. Now, this pressure may be altered fromoutside by changing the initial compression of the spring. In thepresent system, the initial compression of the spring may be changed bymeans of a pilot valve 29 (FIG. 3) provided at the control station ofthe submarine craft. The pilot valve 29 and the valve 27 are ofidentical design. The compression spring 30 of the pilot valve can bemanually adjusted. This adjustment produces a corresponding adjustmentof the pressure existing in a supply line 32 which is connected to theoverflow valve 27. The pressure existing in the supply line 32 isapplied to that side of the piston in the overflow valve 27 which isexposed to the action of the compression spring so that it assists theaction of the spring. The supply line 32 is supplied with hydraulicfluid through a branch line 33 which incorporates a throttle 34. Througha leakage line 35, the hydraulic fluid is returned from the pilot valve29 to the hydraulic fluid tank 5 shown several times in FIG. 3.

Apart from the overflow valve 27, the control device 7 also comprisesthe reversing valves 36, 37 and 38 which in their central position ofrest shown in FIG. 3 interrupt the supply of hydraulic fluid to thedrive motors 12, 10 and 15. Depending on the control setting at anytime, the respective motor will rotate clockwise or counterclockwise.From each reversing valve, one return line (diagrammatically representedas return line 8 in FIG. 1) leads to the hydraulic fluid tank 5 viaadjustable throttles 39, 40 and 41.

In addition to the drive motors 10, 12 and 15 for the main and steeringpropellers, further control and regulating devices may be connected tothe hydraulic sysconnected via a non-return valve 42. A throttle 44which may be connected to a hydraulic bladder accumulator 46 via areversing valve 45 is connected at the liquid end of the hydraulicaccumulator 43. The interior of the bladder accumulator 46 is dividedinto two separate spaces by means of a flexible partition 47. One ofthese spaces is connected to the hydraulic system via the reversingvalve 45 while the other of these two spaces is connected to the outsidethrough a line 48 which leads into the outboard water. When hydraulicfluid is supplied to the bladder accumulator 46 via the reversing valve45, water is expelled from the other space of the bladder accumulator 46so that the weight of the craft is reduced and its positive buoyancyincreased. When, conversely, the space of the bladder accumulator 46filled with hydraulic fluid is connected to the hydraulic fluid tank 5by a switch-over of the reversing valve 45, the external pressure forceswater through the line 48 into the bladder accumulator 46, causing thehydraulic fluid contained in the other space of the bladder accumulator46 to flow into the hydraulic fluid tank 5. This inflow of waterincreases the weight of the craft and reduces its positive buoyancy. Bymeans of this arrangement, the buoyancy of the craft may be adjustedwithin very fine limits.

In a submarine craft, the center of gravity may be shifted, e.g. whenone of the crew changes his position inside the craft. This would causethe craft to deviate from its desired horizontal or almost horizontalposition. To compensate such deviation, a trim device is provided bymeans of which weights are shifted so as to restore the desired trim,i.e. the desired position of the craft with respect to the horizontal.To this end, a manual change-over valve 50, which takes the form of athree-way valve, is connected to the hydraulic energy supply system viaa supply line 49. In one position, the said manual change-over valveconnects the supply line 49 with a reversing valve 51 which has acentral position of rest and two control positions. In the position ofrest, the flow is shut off. In the one control position, hydraulic fluidflows to a power cylinder 53 through the reversing valve 51 and acontrol line 52. In the power cylinder 53 there is provided a slidablepiston 54 which moves relatively to the said cylinder and, through acompensating line 55, admits hydraulic fluid to a fur- 'ther powercylinder 56 in which a piston 57 is slidably guided which, when moved,forces hydraulic fluid to the hydraulic fluid tank 5 via a leakage line58, the reversing valve 51 and a further line 59 with an active,adjustable throttle 60. When the reversing valve 51 is moved to itsother control position, hydraulic fluid from the supply line 49 flows toline 58 via the manual change-over valve 50 and through the reversingvalve 51 and hydraulic fluid from the power cylinder 53 flows throughline 52 to line 59 and on to the hydraulic fluid tank 5. In this case,the two pistons 54 and 57 are moved in opposite directions. The pistonsare coupled to heavy masses which may thus be moved in oppositedirections to adjust the desired trim. The manual changeover valve 50may have connected to it a hand pump 61 which enables the trim device tobe operated manually in the event of a failure of the hydraulic energysupply system by manually pumping hydraulic fluid to the reversing valve51.

To prevent mechanical impurities of the hydraulic fluid from enteringthe hydraulic energy supply system, a filter 62, which cleans thehydraulic fluid sucked from the hydraulic fluid tank 5, is disposedupstream of the pump 3.

FiG. 2 shows a longitudinal section through a propulsion unit. Eachpropulsion unit comprises a fixed hub section 63 in the form of a hollowcylinder with three integrally cast fins 64 spaced at angles of l20each.By the fins 64 the propulsion units may be fastened to the submarinecraft, sound-deadening flexible elements being interposed between thefins and the hull. Each fin and the associated flexible elements areprovided with four bores 65, 66, 67 and 68. The hydraulic bores 65 and66 serve to supply and return hydraulic fluid to and from the hydraulicmotor 10 which is accommodated within the hub section 63. The leak-waterbore 67 serves to drain any leak water entering the unit while theleakage bore 68 drains any hydraulic fluid leaking from the hydraulicmotor 10.

The output shaft 69 of the hydraulic motor 10 is coupled to anintermediate shaft 70 in a manner preventing relative rotation. Theintermediate shaft 70 is supported in a ball bearing 71 fitted in abearing sleeve 72 provided in the bearing sleeve 72 which ends in anannular space 77 surrounding a central portion of the intermediate shaft70. Between the annular space 77 and the ball bearing 71 there areprovided two sliding sealing rings 78 which seal the annular space 77with respect to the ball bearing 71. A slide ring 79 on the intermediateshaft 70 serves as an axial backing for a support ring 80 which, inturn, has a shoulder forcing an O-ring 81 against a shoulder 82 of thebearing sleeve 72. The O-ring 81 provides a tight seal for the annularspace 77 towards the outside. Water which leaks past the slide ring 79enters the annular space 77 whence it flows, without pressure, to theleak-water collecting tank 22 through the leak-water bore 76, theleak-water bore 67 and the leak-water line 19. A bearing cap 83, whichis provided with bores and forms a waterlubricated plastic bearing forthe propeller shaft, is screwed to the end of the bearing sleeve 72. Thebores provided in the bearing cap 83 as well as the bearing sleeve 72ensure adequate cooling of the slide ring seal 79 by means ofcirculating water. The hemispherical end cap of a hollow hub 84 to whichthe blades of the propeller 11 are secured, e.g. as integral castings,is screwed to the free end of the intermediate shaft 70.

It shall be understood that the present invention is not restricted tothe embodiment shown by way of example and that deviations therefrom arepossible within the scope and spirit of the invention. In particular, itshall be understood that individual features of this invention may beemployed either severally or in combination.

One advantage of the propulsion system in accordance with this inventionconsists in that a leak-water collecting chamber is disposed downstreamof the shaft seal which seals the system off from the high externalpressure, whereby the seal towards the interior of the motor is totallyor largely relieved of pressure. In case of damage to thepressure-loaded shaft seal, the entry of leak water from the leak-watercollecting chamber into the pressure hull may readily be prevented byclosing the relevant shut-off valve 23 in line 19, 20 or 21.

What is claimed is:

l. A submarine craft comprising: a tight pressure hull, an electricenergy source, a plurality of propellers, each of said propellers beingprovided with a drive shaft, hydraulic motor means for driving each ofsaid propellers, a hydraulic energy transmission system in cludingconverter means operatively connected with said electric energy sourcefor converting said electric energy to hydraulic energy, meansoperatively connected with said converter means for supplying hydrau:lic energy to said hydraulic motor means. said hydraulic motor meansincluding an axial piston motor for driving each of saidplurality ofpropellers, a housing surrounding each of said motors, the surface ofsaid housing being in direct heat contact with the water flowingtherearound, each of said propellers and each of said motors beingcombined into a single structural unit disposed outside of said pressurehull, means for sealing each of said drive shafts toward the interior ofsaid motor, a sliding ring seal, a leak-water collecting chamberprovided on a side of said ring seal which faces the water, and aleak-water tank operatively connected to said leak-water collecting chtrnbegsaid leakwater tank having an inter'nal pressure which is alwaysless than the pressure permitted for said sliding ring seal.

2. A submarine craft as claimed in claim 1, wherein said electric energysource includes electric storage batteries and wherein said convertercomprises an electric motor and a hydraulic pump.

3. A submarine craft as claimed in claim 1, further comprising a trimmeans operatively connected with said transmission system for changingthe center of gravity of the craft.

4. A submarine craft as claimed in claim 1, further comprising abuoyancy means operatively connected with said hydraulic energytransmission system for fine adjustment of the buoyancy of the craft,said buoyancy means comprising a vessel means for admitting water intosaid vessel to change the buoyancy and means for admitting hydraulicfluid into said vessel for expelling water from said vessel.

5. A submarine craft as claimed in claim l,-wherein a propeller shaftbearing is provided adjacent to the sliding ring seal and accommodatedin said housing.

6. A submarine craft as claimed in claim 1, wherein at least one of flowcontrol valves or chage-over valves are provided to control at least one'of the speed or sense of rotation of said hydraulic axial pistonmotors, said valves being operatively connected with a respectivehydraulic axial piston motor.

7. A submarine craft according to claim 1, wherein a mounting means isprovided for mounting said hydraulic motor means exteriorly of saidpressure hull and wherein said mounting means constitute said housingwith a portion of said axial piston motor disposed therein.

1. A submarine craft comprising: a tight pressure hull, an electricenergy source, a plurality of propellers, each of said propellers beingprovided with a drive shaft, hydraulic motor means for driving each ofsaid propellers, a hydraulic energy transmission system includingconverter means operatively connected with said electric energy sourcefor converting said electric energy to hydraulic energy, meansoperatively connected with said converter means for supplying hydraulicenergy to said hydraulic motor means, said hydraulic motor meansincluding an axial piston motor for driving each of said plurality ofpropellers, a housing surrounding each of said motors, the surface ofsaid housing being in direct heat contact with the water flowingtherearound, each of said propellers and each of said motors beingcombined into a single structural unit disposed outside of said pressurehull, means for sealing each of said drive shafts toward the interior ofsaid motor, a sliding ring seal, a leak-water collecting chamberprovided on a side of said ring seal which faces the water, and aleak-water tank operatively connected to said leak-water collectingchanger, said leak-water tank having an internal pressure which isalways less than the pressure permitted for said sliding ring seal.
 2. Asubmarine craft as claimed in claim 1, wherein said electric energysource includes electric storage batteries and wherein said convertercomprises an electric motor and a hydraulic pump.
 3. A submarine craftas claimed in claim 1, further comprising a trim means operativelyconnected with said transmission system for changing the center ofgravity of the craft.
 4. A submarine craft as claimed in claim 1,further comprising a buoyancy means operatively connected with saidhydraulic energy transmission system for fine adjustment of the buoyancyof the craft, said buoyancy means comprising a vessel means foradmitting water into said vessel to change the buoyancy and means foradmitting hydraulic fluid into said vessel for expelling water from saidvessel.
 5. A submarine craft as claimed in claim 1, wherein a propellershaft bearing is provided adjacent to the sliding ring seal andaccommodated in said housing.
 6. A submarine craft as claimed in claim1, wherein at least one of flow control valves or chage-over valves areprovided to control at least one of the speed or sense of rotation ofsaid hydraulic axial piston motors, said valves being operativelyconnected with a respective hydraulic axial piston motor.
 7. A submarinecraft according to claim 1, wherein a mounting means is provided formounting said hydraulic motor means exteriorly of said pressure hull andwherein said mounting means constitute said housing with a portion ofsaid axial piston motor disposed therein.